1. Field of the Invention
This invention relates to a fluid dynamic bearing unit and a drive device for a recording disk. In addition, this invention relates to a method of manufacturing a fluid dynamic bearing unit.
2. Description of the Related Art
In recent years, disk drive devices such as HDDs have included fluid dynamic bearing units (abbreviated to FDBs) to enhance disk drive performances. Generally, a disk drive device capable of rotating a recording disk at a higher speed is desired. In a conventional disk drive device for magnetically recording data on a recording disk, the speed of rotation of the disk is 3600 min−1. Recent disk drive devices rotate recording disks at a speed of 5400 min−1 or 7200 min−1.
In a disk drive device, higher-speed rotation of a recording disk causes greater unwanted vibration of a magnetic head which disturbs the tracing of a recording track by the magnetic head. A known disk drive structure designed as a countermeasure for this problem includes an FDB having a shaft, one end of which is fixed to a base. In the known structure, the shaft less vibrates so that the tracing of a recording track by a magnetic head can be prevented from being unacceptably disturbed.
Such a disk drive structure typically includes two capillary seals provided at two ends or sides of an FDB respectively. When lubricant is injected into the FDB via one of the capillary seals, air bubbles tend to be drawn thereinto via the other capillary seal. The lubricant can not easily move into a narrow clearance in the FDB. Therefore, charging the FDB with the lubricant tends to take a long time. During a longer-time charging process, more air bubbles are drawn into the FDB. Air bubbles in the FDB reduce bearing stiffness. A reduction in bearing stiffness may cause an FDB malfunction. In the event that the amount of the lubricant in the FDB is insufficient, the life of the FDB may be short. Accordingly, it is desirable to check the amount of the lubricant in the FDB.
PCT application publication number WO 96/25606 discloses a hydrodynamic bearing which takes a cylindrical shape. The hydrodynamic bearing has a stationary shaft, one end of which is coupled to a thrust plate forming a part of a base. The hydrodynamic bearing has two capillary seals at two ends thereof. One of the capillary seals is inverted while the other is non-inverted. The two capillary seals have upwardly-facing open ends respectively.